1. Field of the Invention
The present invention relates to a transport apparatus for bringing a semiconductor substrate or the like into a vacuum processing chamber and carrying it out from the chamber to a predetermined position.
2. Description of the Related Art
In recent years, there has been a strong demand for precision semiconductor devices with critical dimensions. Systems for manufacturing such semiconductor devices are then required to improve the throughput and reduce the foot print necessary for installing the system.
In view of these requirements, there have been proposed multi-chamber systems and transport apparatuses comprising a transport chamber arranged at the center and a plurality of processing chambers arranged around the transport chamber and connected thereto by way of respective gate valves so that various processing operations may be conducted in vacuum atmosphere in a coordinated manner (see the publications of Japanese Patent Nos. 2733799 and 2808826).
FIG. 16 of the accompanying drawings is a schematic plan view of such a known transport apparatus (as disclosed in Japanese Patent Laid-Open Publication No. Hei. 4-279043), illustrating a principal part thereof.
Referring to FIG. 16, in the transport apparatus 100, the rotary force generated by a drive source (not shown) is transmitted to a drive shaft 101, to a drive gear 102 secured to the drive shaft 101 and then to a driven shaft 104 by way of driven gear 103 engaged with the drive gear 102.
A first arm 105 is fitted to the drive shaft 101 and a third arm 107 is linked to the end of the first arm 105 so as to be rotatable around its rotary shaft 106.
On the other hand, a second arm 108 is fitted to the driven shaft 104 and a fourth arm 110 is linked to the end of the second arm 108 so as to be rotatable around its rotary shaft 109.
A movable pulley 111 is fitted to the third arm 107 so as to be rotatable coaxially around the rotary shaft 106. The movable pulley 111 is linked to a fixed pulley 112 that is fixed coaxially with the driven shaft 101 by way of a belt 113. The diameter of the movable pulley 111 and that of the fixed pulley 112 show a ratio of 1:2.
Mating gears 116, 114 are rotatably fitted to the respective ends of the third and fourth+arms 107 and 110. The mating gears 116, 114 are engaged with each other and fitted to a substrate holder 115.
With the known transport apparatus 100 having the above described link mechanism, as the drive shaft 101 is driven to rotate, the substrate holder 115 is moved along a straight line 1 rectangularly intersecting the straight line connecting the center of the drive shaft 101 and that of the driven shaft 104 (to be referred to as “transport line” hereinafter) in a horizontal plane and passes through a position where the first arm 105 and the second arm 108 form an angle of 180° (to be referred to as “dead point” hereinafter).
In the transport apparatus 100, the drive shaft 101 and the driven shaft 104 are rotatably fitted to a support (not shown) in such a way that the substrate holder 115 is driven to rotate around the drive shaft 101 by another drive source (not shown).
With the above described known transport apparatus 100, however, since the substrate holder 115 is driven to rotate around the drive shaft 101, it does not rotate around the center of the arms that is the intersection O of the straight line m connecting the center of the drive shaft 101 and that of the driven shaft 104 and the transport line 1 when the first through fourth arms 105, 107, 108 and 110 are folded to the dead point.
This means that, with the above described known transport apparatus 100, it is difficult to reduce the minimum turning radius and hence the inner diameter of the transport chamber. Then, by turn, it is difficult to dimensionally reduce the entire semiconductor manufacturing system.
While the throughput of a semiconductor manufacturing system can be improved effectively by increasing the operating speed of the transport apparatus thereof, the operating torque of the drive source cannot be raised to increase the operating speed of the transport apparatus when both the drive shaft 101 and the driven shaft 104 are operated by means of a single drive source as in the case of the above described known transport apparatus. This problem is due to transmission loss of rotary force.
These problems may be solved by using first and second drive shafts that are arranged coaxially and driven independently by respective drive sources. Then, however since the mating gears 114, 116 that constitute an articulating mechanism are juxtaposed, the angle of rotation of the third arm 107 relative to the first arm 105 and that of the fourth arm 110 relative to the second arm 108 are not proportional to the angle of rotation of the first arm 105 and that of the second arm 108 respectively. Therefore, the rotary motion of the third arm 107 and that of the fourth arm 110 are not synchronized with the rotary motions of the first and second arms 105, 108 to make it difficult to move the substrate holder 115.
While these problems may be avoided by providing a complex correction mechanism, such a mechanism inevitable raise the number of components and that of assembling steps.
FIG. 17 of the accompanying drawings is a schematic plan view of another known transport apparatus (as disclosed in Japanese Patent Laid-Open Publication No. Hei. 9-283588), illustrating a principal part thereof.
Referring to FIG. 17, with this known transport apparatus 200, the rotary forces generated independently by a pair of drive sources (not shown) are transmitted respectively to a first drive shaft 201 and a second drive shaft 202 that are arranged coaxially.
A first arm 203 is fixed to the first drive shaft 201 and a third arm 205 is linked to the end of the first arm 203 so as to be rotatable around its rotary shaft 207.
On the other hand, a second arm 204 is fixed to the second drive shaft 202 and a fourth arm 206 is linked to the end of the second arm 204 so as to be rotatable around its rotary shaft 208. The length of the second arm 204 and that of the fourth arm 206 are made equal to those of the first and third arms 203 and 205, respectively.
A first pulley 209 is fixed to the third arm 205 so as to be rotatable around the rotary shaft 207 coaxially. A second pulley 210 is coaxially fixed to the second drive shaft 202. An endless drive belt 211 is wound around the first pulley 209 and the second pulley 210. A dead point escape mechanism 212 is formed by the first and second pulleys 209, 220 and the drive belt 211.
A first mating pulley 215 is fixed to the end of the third arm 205 and a second mating pulley 216 having a diameter same as that of the first mating pulley 215 is fitted to the end of the fourth arm 206. The first and second mating pulleys 215, 216 are rotatably fitted to a substrate holder 217 by way of respective rotary pins 219, 220. A restraint belt 221 is wound around the restraint pulleys 215, 216 to substantially form a FIG. “8”. The first and second mating pulleys 215, 216 and the restraint belt 221 form an attitude control mechanism 222.
With this known transport apparatus 200 having the above described link mechanism, the substrate holder 217 is driven to move straight by rotating the first drive shaft 201 and the second drive shaft 202 reversely relative to each other on the transport line 222 passing through the bisector of the angle between the third arm 205 and the fourth arm 206 running through the center of the first drive shaft 201 and the second drive shaft 202, the angle being restraint by the restraint belt 221.
With this known transport apparatus 200, if the first arm 203 and the second arm 204 are located on dead line 223 where the angle between the first arm 203 and the second arm 204 becomes equal to 180°, the rotary force of the second drive shaft 202 is transmitted to the third arm 205 by way of the drive belt 211 and the first pulley 209 to cause the substrate holder 217 to pass through the dead line 223.
Additionally, with this known transport apparatus 200, since the fourth arm 206 is linked to the second arm 204 by means of a pin (whereas the third arm 205 is not only linked to the first arm 203 by means of a pin but also restrained by the second drive shaft 202 by way of the first pulley 209, the drive belt 211 and the second pulley 210). the first pulley 209 and the third arm 205 try to rotate relative to the first arm 203 by an angle of 2 θ (that is, twice the rotary angle θ of the second arm 204) when the first drive shaft 201 and the second drive shaft 202 are driven to rotate in opposite senses by an angle of θ.
On the other hand, since the two mating pulleys 215, 216 of the attitude control mechanism 222 are juxtaposed, the angle of rotation of the third arm 205 relative to the first arm 203 and that of the fourth arm 206 relative to the second arm 204 are not proportional to the angle of rotation θ of the first and second arms 203 and 204. In other words, since the angle of rotation of the mating pulley 215 is equal to that of the mating pulley 216, the former angles of rotation are not equal to twice of the angle θ and the constant of proportionality can fluctuate around 2 depending on the latter angles of rotation. Because of the discrepancy that can arise to the angle of rotation of the third arm due to the different mechanism, the substrate holder 217 may not be held uniformly relative to the transport line 222; thereby, deteriorating the straightness of the movement. Additionally, the substrate holder 217 may have difficulty in moving.
It is known to divide the drive belt 211 and arrange tension coil springs between them in order to avoid the above identified problems. It is also known to provide a tension regulating mechanism for suppressing the expansion/contraction of the drive belt 211 by arranging a plurality of tension pulleys between the first pulley 209 and the second pulley 210.
However, even the known transport apparatus 200 is provided with such a known tension regulating mechanism, the first pulley 209 and the second pulley 210 can show a phase difference because of the difference in the elongation due to heat of the drive belt 211 and the first arm 203 so that the dead point escape mechanism 212 can still adversely affect the linear movement of substrates. This problem is particularly remarkable when the arms of the link mechanism and the drive belt 211 are made long in order to increase the distance for transporting substrates. Additionally, the tension regulating mechanism involves a problem of requiring a long and cumbersome operation for assembling it and regulating the tension.
It is also known to provide a mechanism designed to equalize the angle or rotation of the fourth arm 206 relative to the second arm 204 and that of the third arm 205 relative to the first arm 203 by using a cam-shaped pulley for the first pulley 209 or the second pulley 210 and restricting the rotary motion of the third arm 205 in order to ensure a linear movement of the known transport apparatus 200.
However, if such a cam-shaped pulley is used for the transport apparatus 200, the process of preparing the cam-shaped pulley becomes a cumbersome one and requires an increased number of parts to consequently raise the cost of the mechanism and hence that of the semiconductor manufacturing system including the transport apparatus 200.
While it may be conceivable to provide a mechanism for adjusting the length of the first arm 203, again the process of preparing such a mechanism is cumbersome and requires an increased number of parts to consequently raise the cost of the mechanism as in the case of the tension regulating mechanism and the pulley mechanism, which are described above.